Why a plant would need to break down its own walls
Cellulose is the tough fiber that gives plant cell walls their strength. A cellulase is simply an enzyme that cuts cellulose into smaller pieces. It might seem odd for a plant to carry tools that dismantle its own scaffolding, but cell walls are not static—they must stretch and rearrange as a cell grows. Plant cellulases are involved in loosening the cell wall during cell expansion, which lets the wall yield as the cell gets bigger [1].
The same kind of wall-loosening shows up in fruit. As fleshy fruit ripens, its cell walls are broken down by enzymes, and the tissue softens. In bilberry, researchers identified 20 cellulase genes from the GH9 family—a group of related cellulose-cutting enzymes—and four of these were switched on specifically during fruit ripening, consistent with a role in softening [2].
What plant cellulases actually do in the lab
The bilberry work went beyond spotting genes. When the four ripening-related cellulases were produced and tested, all of them showed activity against cellulose and hemicellulose—another wall component—and one, VmGH9C1, was especially active, breaking down cellulose, xyloglucan, and glucomannan [2]. These enzymes were also secreted and carried a carbohydrate-binding module, a small attachment that helps an enzyme stick to its target [2].
That study also found the enzymes kept working across a wide pH range (6–10) and at high temperatures, with an optimum around 70 °C [2]. Those are laboratory measurements on isolated enzymes, not proof of what happens inside a living bilberry, but they show the enzymes are genuine, functional cellulose-cutters.
Plant cellulases are real but less studied than microbial ones
Most commercial and industrial cellulases come from microbes, and the bilberry authors note that cellulases also exist in plants but are less studied [2]. The food-processing review makes a related point: animals do not possess cellulases, while plant cellulases serve roles such as cell-wall loosening during growth [1]. So the ability to make cellulase is not limited to microbes—plants have their own versions.
This matters practically. Because plant cellulases can degrade cellulose and hemicellulose, the bilberry authors suggest they could be useful in industrial processing of plant fiber [2]. That is a proposed application, not a demonstrated one, but it follows from the measured enzyme activity.
Cellulases at work when plant material is fermented
Cellulases also appear in the fermentation of woody plant material. In mulberry silage, a combination of cellulase and lactic acid bacteria acted together: cellulases such as carboxymethyl cellulase broke cellulose and hemicellulose down into sugars, and the bacteria converted those sugars into lactic acid, improving the fermentation [4]. The abstract describes this synergy in the silage system rather than establishing where each enzyme originated, so it is best read as evidence that cellulase activity is central to breaking down plant walls in this process.
Sources used in this answer
Cellulases in food processing
Plant cellulases are involved in loosening cell walls during plant cell expansion, and animals do not possess cellulases.
Characterization of cellulases from softening fruit for enzymatic depolymerization of cellulose
Bilberry has 20 GH9 cellulase genes, four expressed specifically during fruit ripening and linked to softening; the recombinant enzymes showed activity against cellulose and hemicellulose and retained activity across pH 6–10 with an optimum near 70 °C.
Production Of Cellulase In Plastids Of Transgenic Plants
Transgenic plants can be engineered to produce cellulase targeted to plastids, where it can be collected and purified.
Cellulase–lactic acid bacteria synergy action regulates silage fermentation of woody plant
In mulberry silage, cellulases and lactic acid bacteria acted synergistically, with cellulases breaking cellulose and hemicellulose into sugars that bacteria converted to lactic acid.
New nanostructured carriers for cellulase immobilization
Cellulase is a multienzyme complex that breaks down cellulose in plant cell walls, and immobilizing it on nanostructured carriers can improve its stability and efficiency for converting plant biomass.